I have heard of the hum problem with that particular amp, and I believe that it can be fixed. Are you aware that there was an "A" revision also? You should call Conrad Johnson and inquire. That is a great amp. I auditioned it once for a couple of hours, and thought it was extremely musical.
Any way to "improve" a Conrad Johnson MF 2500
I recently purchased a 10 year old CJ MF2500 amplifier. It is in perfect condition and it sounds excellent, but I noticed a hum coming from my speakers when it is turned on. It got me thinking, since there is no way to upgrade the power cord, if there was a way to "refurbish" or update the amp. I don't know if that is something normal for a solid state amp, but it's sounds so good and is in such good shape that I thought I would see what the rest of you thought. It would be nice to see it work for another ten years.